Storage-stable aerated gel composition and a process for producing it

ABSTRACT

A storage-stable aerated gel composition comprising 30 to 97% by weight of water, 0.2 to 5% by weight of a gelling agent selected from xanthan gum, sodium alginate and neutralized carboxyvinyl polymer and 2 to 5% by weight of a fine particulate hydrophobic silicone-treated silica having a surface area of from 80 to 300 m 2 /g. The composition is in the form of fine particles of an aqueous gel containing the water and the gelling agent, the surface of which particles are coated with a coating of the finely divided particulate hydrophobic silica. The gel composition is prepared by mixing, under high shear conditions, the water and the fine particulate silica, and then adding to the resulting mixture, the gelling agent and mixing under high shear conditions.

This application is a 371 of PCT/GB 00/04340 filed Nov. 15, 2002.

The present invention relates to storage-stable aerated gelcompositions. It also relates to a process for making such compositions.In particular, the gel compositions contain a particular hydrophobicsilica, water and gelling agent.

Aqueous dispersions of silica can be prepared into a state knowngenerally in the prior art as “dry water”. In fact “dry water” is knownin two forms. The first form can be produced by absorbing aqueousliquids onto hydrophilic material to form a material which exists asfree-flowing powder or granules. The second form can be produced bycoating finely divided aqueous liquids with powdered hydrophobicmaterial, such as metal oxides. Each liquid particle in this second formof “dry water” is separated from the next by a hydrophobic metal oxidecoating and by air spaces. Very high speeds of, for example, over 6000rpm, and mixing times of 15 minutes are typically required. This secondform is, however, thermodynamically unstable and, when produced, tendsto break down after a relatively short period of time.

The present invention is based on the discovery that stable aerated gelsanalogous to this second form of “dry water” can be produced.

The present invention provides a storage-stable aerated gel compositioncomprising 30 to 97% by weight of water, 0.2 to 5% by weight of agelling agent selected from xanthan gum, sodium alginate and neutralisedcarboxyvinyl polymer and 2 to 5% by weight of a fine particulate,hydrophobic silicone-treated silica having a surface area of from 80 to300 m²/g which said composition is in the form of fine particles of anaqueous gel containing the water and gelling agent, the surfaces ofwhich fine particles are coated with a coating of the finely particulatehydrophobic silica.

The present invention further provides a process for producing astorage-stable aerated gel composition which comprises the steps ofmixing, under high shear conditions, from 2 to 5% by weight of a finelyparticulate, hydrophobic silicone-treated silica having a surface areaof from 80 to 300 m²/g and from 30 to 97% by weight of water, adding tothe resulting mixture from 0.2 to 5% by weight of a gelling agentselected from xanthan gum, sodium alginate and neutralised carboxyvinylpolymer and mixing the gelling agent with the silica-water mixture underconditions of high shear.

A discovery on which the present invention is based lies in the use ofcertain gelling agents which, when added to a premix formed by mixingthe water and a specific type of hydrophobic silica under high shearconditions and then mixed with the premix also under high shearconditions, give a storage-stable aerated get composition. Manyconventional gelling agents which are ordinarily used to gel aqueoussystems do not produce storage-stable gel compositions according to thepresent invention. The reasons for this are not, at present, understood.Furthermore, by adjusting the components used in the present inventionthe structure of the gel composition produced can be varied from afree-flowing pulverulent fluid composition which may have applicationsusing conventional spray or dusting equipment to a non-flowingcomposition which may have applications as a caulking material.

Where the words “comprises” or “comprising” are used herein, it isintended that these may have the meaning “includes” and “including”,respectively, to the extent that the presence of one or more othermaterials is not excluded.

The composition of the present invention comprises a fine particulatehydrophobic silicone-treated silica having a surface area of from 80 to300 m²/g. By the term “fine particulate”, as applied to the hydrophobicsilica, it is meant that the hydrophobic silica will typically have anaverage particle size of less than 40 μm. The silica used is one thathas been rendered hydrophobic by surface treatment using one or moreorganosilicon compounds to produce, on the silicon dioxide surface,silicone groups. The technique of hydrophobicizing silica in this way iswell-known and such silicone-treated silica is available commercially.We have found that good results are obtained by using hydrophobic silicamarketed under the name CAB-O-SIL (“CAB-O-SIL” is a trademark of CabotCorporation), preferably CAB-O-SIL TS720. However, othersilicone-treated silicas can also be used in the present invention ifthey have a surface area within the range of from 80 to 300 m²/g. Thehydrophobic silica may also be one that has been surface treated toproduce siloxane, as well as, silicone groups attached to the silicondioxide surface.

The hydrophobic silica is used in an amount of from 2 to 5% by weightbased on the total weight of the composition. The use of greater than 5%by weight of the hydrophobic silica results in a gel composition whichis excessively dusty. The use of such a composition may give rise to agreater nuisance dust risk. Preferably, the amount of hydrophobic silicawill be in the range of from 3 to 4% by weight of the composition.

The water used may typically be tap water although purified grades maybe appropriate for some applications. The water will normally be used atambient temperature since there appears to be no advantage in usingheated or cooled water in the performance of the invention. The watergenerally will form from 30 to 97% by weight of the total composition.Preferably, however, the amount of water will be from 90 to 97% byweight to ensure the formation of aerated gel compositions of goodconsistency and improved stability.

As mentioned above, the gelling agent is one or more selected fromxanthan gum, sodium alginate and neutralised carboxyvinyl polymers, suchas carboxypolymethylene neutralised with triethanolamine. These gellingagents are included in an amount of from 0.2 to 5% by weight. The use ofan amount greater than 5% by weight of the gelling agent results in agel composition having an excessively high gel strength. Preferably,from 0.5% to 2% by weight of the gelling agent will be used depending onthe desired stability and structure of the gel composition. Otherhydrophilic or hydrophobic additives, known to those skilled in the artmay be incorporated to modify the physical or biological properties ofthe composition.

The process for producing the gel compositions involves mixing the waterwith the silica under high shear conditions typically for a few minutes,for example 2 to 5 minutes. The mixing at this stage in the process mustbe carried out under high shear conditions, i.e., conditions which causethe water to be finely fragmented into minute droplets which becomedispersed within the finely particulate hydrophobic silica such that thesurfaces of the water droplets become coated with the hydrophobic silicaparticles. The term “high shear” is, of course, well-known to the personskilled in the art of mixing or blending and whether or not a particularmixing apparatus is capable of mixing aqueous compositions under highshear conditions will be known to one skilled in the art. This may beachieved by using standard high speed mixers, typically using a mixingspeed of at least 2000 rpm and generally from 2000 to 3000 rpm. Afterthe hydrophobic silica and the water have been mixed to create adispersion of fine droplets of water in the silica, the gelling agent isadded and mixing at high speed is continued for several minutes untilthe gelling agent has been thoroughly incorporated into the liquidphase. It is preferred in the present invention to add the gelling agentafter the silica and water have been thoroughly mixed together. If thegelling agent is added before the silica, mixing requires more energyand the homogeneity and stability of the resulting gel composition canbe compromised.

The storage-stable aerated gel compositions of the present invention canbe used in sprayable formulations produced for domestic, veterinary,agricultural or horticultural applications.

The invention will now be illustrated by the following examples in whichthe compositions in Examples 1 to 3 and 5 to 7 were mixed using an IKARE166 high speed mixer having a radial flow toothed disc mixer head andthe composition in Example 4 was mixed using a larger scale Torrancehigh speed mixer having a radial flow toothed disc mixer head.

EXAMPLE 1

Cold tap water 95.5 g was mixed with 3 g of CAB-O-SiL TS720 (silica) at2800 rpm on the laboratory mixer for 2 minutes. “Dry water” was notformed. Powdered xanthan gum 1.5 g was added and the mixer speedincreased to 5500 rpm for a further 3 minutes. A free-flowing aeratedgel was formed with a density of 0.6 g/ml. No water separated on storageat laboratory ambient (max/min 30/8° C.) at 24 weeks.

EXAMPLE 2

Cold tap water 96.5 g was mixed with 3 g of CAB-O-SIL TS720 at 2800 rpmon the laboratory mixer for 2 minutes. “Dry water” did not form.Powdered xanthan gum 0.5 g was added and the mixer speed increased to5500 rpm for a further 3 minutes. A free-flowing aerated gel was formedsimilar in appearance to that formed in Example 1. The gel compositionformed in this Example could be syringed through a 0.26 mm internaldiameter needle but blocked a 0.21 mm internal diameter needle.

EXAMPLE 3

Using a larger mixing vessel with the laboratory mixer 1930 g of coldtap water, 60 g of CAB-O-SIL TS720 and 10 g of powdered xanthan gum weremixed by the same process as described in Example 2. The product wasidentical to that produced in Example 2. A 1 liter sample wastransferred to a 2 liter PET bottle and held under 1.7 bar pressure.This sample remained stable with no water separation for greater than 31days stored at ambient temperature. Some water separation was notedafter 59 days under continuous pressure. The sample was easilyre-homogenised by 5 vigorous inversions and no further water separateduntil 16 hours later.

EXAMPLE 4

Cold tap water 77.2 kg was mixed with 2.4 kg of CAB-O-SIL TS720 on theproduction mixer at 2500 rpm for 1 minute. “Dry water” did not form.Powdered xanthan gum 0.4 kg was added and mixing continued at the samespeed for a further 10 minutes. The product was a free-flowing aeratedgel as in Examples 1 to 3. Six further 80 kg batches were made by thesame process and recipe without variation in the product. A sample ofthis product 8.6 kg was packed into a polypropylene bucket with atightly fitting lid. This sample was transported in a car for 2022 milesover a duration of 6 weeks. No water separation occurred during thisperiod. At 14 weeks there was 4.7% m/m water separation. Further samplesfrom these production batches were applied as a “wet dust” through aGLORIA 2010 Knapsack sprayer at 2 to 4 bar pressure fitted with a TEEJET65030E brass nozzle. The nozzle filter was removed for theseapplications. A total of 115 liters of dry gel were applied through thisknapsack sprayer without blockage. Further samples were applied as a“wet dust” through a STIHL SR400 motorised mistblower fitted with apressure pump. The tank filter was removed and the standard adjustablespray nozzle was retained for these applications. A total of 250 litersof dry gel was applied through this mistblower at a nozzle setting of 3to 4 without blockage.

EXAMPLE 5

Cold tap water 76.5 g, propylene glycol 20 g and 3 g of CAB-O-SIL TS720were mixed on the laboratory mixer at 2800 rpm for 2 minutes. “Drywater” did not form. Powdered xanthan gum 0.5 g was added and the mixingspeed increased to 5500 rpm for a further 3 minutes. The product was afree-flowing aerated gel of a wetter consistency than in Examples 1 to4. No water separation occurred after 5 days ambient storage.

EXAMPLE 6

Cold tap water 96.3 g and CARBOPOL 980® (registered trademark of BFGoodrich Co.) 0.5 g (a carboxyvinyl polymer) were mixed on thelaboratory mixer at 2800 rpm for 1 minute. CAB-O-SIL TS720 3 g was addedand mixed at the same speed for a further 2 minutes. “Dry water” did notform. Triethanolamine 0.2 g was added to neutralise the CARBOPOL and themixing speed increased to 5500 rpm for a further 3 minutes. A thickpliable aerated dry gel was formed that could be easily extruded througha 30 ml plastic syringe. No water separation occurred after 13 weeksambient storage.

EXAMPLE 7

Cold tap water 96 g and 3 g of CAB-O-SIL TS720 were mixed on thelaboratory mixer at 2800 rpm for 2 minutes. “Dry water” did not form.Sodium alginate, high viscosity grade, 1 g (a polysaccharide) was addedand the mixing speed increased to 5500 rpm for a further 3 minutes. Afree-flowing aerated gel was initially formed which thickened to anon-flowing gel after 5 days. The gel remained pliable and could easilybe extruded from a 30 ml plastic syringe. No water separation occurredafter 6 days ambient storage.

What is claimed is:
 1. A storage-stable aerated gel compositioncomprising 30 to 97% by weight of water, 0.2 to 5% by weight of agelling agent selected from the group consisting of xanthan gum, sodiumalginate and neutralised carboxyvinyl polymer and 2 to 5% by weight of afine particulate, hydrophobic silicone-treated silica having a surfacearea of from 80 to 300 m²/g which said composition is in the form offine particles of an aqueous gel containing the water and gelling agent,the surfaces of which fine particles are coated with a coating of thefinely particulate hydrophobic silica.
 2. A composition according toclaim 1 comprising from 3 to 4% by weight of the silica.
 3. Acomposition according to claim 1 comprising from 90 to 97% by weight ofwater.
 4. A composition according to claim 3 comprising from 3 to 4% byweight of the silica.
 5. A process for producing the storage-stableaerated gel composition which comprises the steps of mixing, under highshear conditions, from 2 to 5% by weight of a fine particulate,hydrophobic silicone-treated silica having a surface area of from 80 to300 m²/g and from 30 to 97% by weight of water, adding to the resultingmixture from 0.2 to 5% by weight of a gelling agent selected from thegroup consisting of xanthan gum, sodium alginate and neutralisedcarboxyvinyl polymer and mixing the gelling agent with the silica-watermixture under conditions of high shear.
 6. A process according to claim5, further comprising mixing the gelling agent with the silica and thewater at a mixing speed of 5000 to 6000 rpm.
 7. A process according toclaim 5, further comprising mixing together the water and the silica ata mixing speed in the range of 2000 to 3000 rpm.
 8. A process accordingto claim 7, further comprising mixing the gelling agent with the silicaand the water at a mixing speed of from 5000 to 6000 rpm.
 9. A processaccording to claim 5, wherein the gelling agent is xanthan gum.
 10. Aprocess according to claim 9, further comprising mixing together thewater and the silica at a mixing speed in the range of 2000 to 3000 rpm.11. A process according to claim 9, further comprising mixing thegelling agent with the silica and the water at a mixing speed of from5000 to 6000 rpm.
 12. A process according to claim 5, wherein the silicais used in an amount of 3 to 4%.
 13. A process according to claim 12,wherein the gelling agent is xanthan gum.
 14. A process according toclaim 12, further comprising mixing together the water and the silica ata mixing speed in the range of 2000 to 3000 rpm.
 15. A process accordingto claim 12, further comprising mixing the gelling agent with the silicaand the water at a mixing speed of from 5000 to 6000 rpm.
 16. A processaccording to claim 5, wherein the water is used in an amount of from 90to 97% by weight.
 17. A process according to claim 16, wherein thesilica is used in an amount from 3 to 4%.
 18. A process according toclaim 16, wherein the gelling agent is xanthan gum.
 19. A processaccording to claim 16, further comprising mixing together the water andthe silica at a mixing speed in the range of 2000 to 3000 rpm.
 20. Aprocess according to claim 16, further comprising mixing the gellingagent with the silica and the water at a mixing speed of from 5000 to6000 rpm.